Over the lifetime of textile items such as garments, there is a continual degradation in the appearance of the items. This is due to a wide variety of effects including the effect of using the textiles, effects during laundry operations and bleaching by sun and air.
The laundry process itself tends to cause degradation of the appearance of textile items. In particular, repeated laundering of coloured textiles can result in dye being removed from the textile leading to a worn or faded appearance. Furthermore, the dye removed can be transferred, via the wash liquor, into other items present, which can lead to a change in colour of the items in the wash. The appearance and colour of dyed fabrics is also affected by exposure to sunlight and air, which have a bleaching effect and by degradation using use.
Dye fixative materials are frequently used in the textile industry to improve the wash fastness of dyed fabrics. Typically, these materials are cationic polymers which interact with the anionic dyes on the fabric forming a complex with increased substantivity to the fabric. These cationic materials cannot be incorporated in typical laundry detergent compositions, because of the tendency of the cationic material to complex with anionic surfactants which are normally present in detergent compositions. The complexes formed in this way are frequently insoluble and precipitate during the laundering process resulting in reduced cleaning efficiency and ineffectiveness of the dye fixative.
Anti-dye transfer polymers have been used in detergent formulations for many years. These operate by complexing with the dye that has leached into the wash liquor during the laundering process. The anti-dye transfer polymers form a water soluble complex which has a much lower affinity for textile fibres than does the dye molecule alone, and so hold the dye in solution and prevent it from transferring to other textiles and causing discolouration. Typical examples of these materials are polyvinylpyrolidone, polypyridine-N-oxide, polyvinylimidazole and copolymers of these materials.
There are two problems associated with anti-dye transfer polymers of this type. They do not prevent the loss of dye from coloured fabrics (they can actually increase this loss and enhance the fading of the colour of the article). Secondly, the materials are not generally particularly effective in detergent compositions containing high levels of anionic surfactant.
The present inventors have discovered that certain polymeric fabric rebuild agents which undergo a chemical change during the laundry process to increase their affinity for fabric can surprisingly reduce dye loss during the laundry treatment of fabrics.
The fabric rebuild agents which are used are themselves the subject of our patent application PCT/EP99/07422. In that patent application, it is realised that the fabric rebuild agents may have dye transfer inhibition properties and may help to reduce fading of colours during the lifetime of garments. However, it was not realised that the fabric rebuild agents would reduce dye loss during laundry treatment of fabrics, particularly in the presence of anionic surfactants.
WO-A-99/14245 discloses laundry detergent compositions containing cellulosic based polymers to provide appearance and integrity benefits to fabrics. These polymers are cellulosic polymers in which the saccharide rings have pendant oxygen atoms to which substituents ‘R’ are bonded, i.e. they are attached to the rings via an ether linkage. The groups ‘R’ can be hydrogen, lower alkyl or alkylene linkages terminated by carboxylic acid, ester or amide groups. Optionally, up to five alkyleneoxy groups may be interspersed between the groups are the respective oxygen atom. At least some of these groups may undergo a chemical change such as hydrolysis, in the wash liquor. However no such change would result in an increased affinity for the fabric. On the contrary, because the “ester” group is configured with the carbonyl group closer to the polysaccharide than the oxygen atom (i.e. esters of carboxyalkyl groups), any hydrolysis will result in free acid substituents which will actually result in an increase in solubility and therefore, a decrease in affinity for the fabric.
WO-A-99/14295 discloses structures analogous to those described in WO-A-99/14245 but in one alternative, the substituents ‘R’ together with the oxygen on the saccharide ring, constitute pendant half-esters of certain dicarboxylic acids. A single example of such a material is given. The dicarboxylic acid half-esters would tend to hydrolyse in the wash liquor and thereby increase affinity of the material for a cotton fabric. However, first, this mechanism of action or behaviour is not mentioned. Second, the hydrolysis rate of such dicarboxylic acids half esters is not as great as that of esters of monocarboxylic acids (which are not disclosed or claimed in WO-A-99/14295) Third, the degree of substitution for this variant is specified as being from 0.001 to 0.1. This is so low as to make the enhancement of fabric affinity too low to be worthwhile for this mechanism of action. Fourth, the structures described and claimed insofar as they have such half ester substituents, must also have substituents of the type which are carboxyalkyl groups or esters thereof, i.e. of the type also described in WO-A-99/14245. In the latter (ester) case, these would hydrolyse to the free acid form. The degree of substitution of the latter (0.2 to 2) is considerably higher than for the half-ester groups and the resultant increase in solubility would easily negate any enhanced affinity for the fabric by hydrolysis of the half-ester groups.
WO 99/14295 indicates that the cellulosic polymers thereof lead to improved overall appearance. Overall appearance is stated to include factors such as formation of lint, fuzz or pills and dye removal. However, it appears that the improved overall appearance is mainly attributable to the reduction in pill/fuzz. There is no evidence that the polymers of WO 99/14295 successfully prevent dye loss during the laundry process.